1. Field of the Invention
The present invention relates to electrophotographic printers. In particular, the present invention relates to a method for controlling power delivered to a fuser assembly of an electrophotographic printer.
2. Description of the Related Art
It is desirable for image forming devices such as printers and scanners to be able to operate in a proper manner irrespective of the variations in the supply line voltage. For proper functioning, it is required that adequate power be supplied to a fuser assembly of an electrophotographic printer to increase the temperature of a heater element in the fuser assembly and enable generation of images soon after powering up the printer. At the same time, it needs to be ensured that excessive power is not delivered to the fuser assembly, since it may result in a catastrophic damage. Therefore, there is a need to control the power delivered to the fuser assembly to account for variations in the supply line voltage and electrical components.
U.S. patent application Ser. No. 11/946,948 describes a method for estimating the heating power delivered to the heater element of the fuser assembly of an image forming device. The method includes application of a predefined portion of a source power to the heater element. Based on this, the rate of increase in temperature of the heater element while being heated from one predefined temperature to another predefined temperature is determined. The rate of increase in the temperature is used to calculate the heating power at the line voltage. Thereafter, the calculated heating power is scaled by a ‘power ratio’ to a baseline heating power configured for proper functioning of the fuser assembly.
For example, 30 percent of the source power is applied to the heater element for heating the heater element of fuser assembly. The heater element is heated from 60° C. to 90° C. The rate of increase in the temperature of the heater element while being heated from 60° C. to 90° C. is measured. Based on the rate of increase in the temperature, the heating power at the line voltage is calculated to be 1200 W. Thereafter, the calculated heating power is scaled to the baseline heating power for the fuser assembly set to 800 W. The ‘power ratio’ for scaling the calculated heating power is determined as given in Equation 1:
                    PowerRatio        ≡                              800            1200                    ×          100          ⁢          %                                    (        1        )            
Power ratio is thus determined to be 66.67 percent from Equation 1.
However, the method described above shows inconsistent results at a constant supply voltage. Empirical tests reveal that the calculated heating power measures higher when the starting temperature of the heater element of the fuser assembly is higher. Table 1 depicts the power ratio that is used to scale the calculated heating power over a series of high and low start temperatures of the heater element of the fuser assembly. Table 2 shows the difference in the power ratio determined at different temperatures of the heater element depicted in Table 1 while keeping the input voltage at a constant level.
TABLE 1Heating power estimationACLOW STARTHIGH STARTINPUTTEMPERATURETEMPERATUREVOLT-POWERPOWERAGETEMPERATURERATIOTEMPERATURERATIO(V)(° C.)(%)(° C.)(%)9021183.41543159.49511525108.3054695.2021352677.0744670.434
TABLE 2Inconsistency in heating power estimationAC INPUTVOLTAGEDIFFERENCE(V)TEMPERATURE (° C.)POWER RATIO (%)9022−23.9211521−13.00313520−6.64For example, at an AC input voltage of 90V, the power ratio is determined to be 183.415 percent at 21° C. and 159.495 percent at 43° C. The difference in the determined power ratio is almost 24 percent over a difference of 22° C. in the temperature of the heater element.
The tests indicate that the initial temperature of the heater element was not taken into consideration while estimating the heating power delivered to the heater element of the fuser assembly.
In light of the foregoing, there is a need to achieve consistency in heating power estimation of the fuser assembly irrespective of the initial temperature of the heater element.